The present disclosure generally relates to processes for removing lactose from dried milk products. More particularly, the present disclosure is directed to processes for removing lactose from dried milk products, and in particular, skim milk powder, to produce dried protein fortified and mineral fortified milk products having reduced lactose. The present disclosure is additionally directed to dried protein fortified milk products with reduced lactose content prepared using these processes.
Skim milk powders, which provide a method of storing and moving surplus skim milk, have conventionally been used by food manufactures for protein fortification of formulated food products. The protein fraction of skim milk powder, which accounts for approximately 36% by weight of the powder, contains caseins and whey proteins in about a 5:1 ratio, respectively. The use of skim milk powders in many of these food applications is limited, however, as the powders include a high lactose content, accounting for approximately 51% to 56% by weight of the powder, which can potentially jeopardize the quality of the final food product through lactose crystallization.
More particularly, the chemical composition of concentrated skim milk prior to spray drying is well beyond the lactose supersaturation point, thus favoring lactose crystallization. Due to the kinetics of the reaction, however, the appearance of the crystals at disenable size is not common during production of skim milk powder. This is attributed to the slow rate of nucleation of the crystals and the conditions typically employed in the production of dried skim milk that disfavor crystal growth. If the concentrated skim milk is held for some time at lower temperatures before spray drying, however, lactose will eventually crystallize.
Previous attempts to overcome the above shortcomings have included turning to the use of dried milk protein concentrates having reduced lactose and mineral contents. The casein and whey protein ratio in milk protein concentrate is typically similar to skim milk powder, allowing the milk protein concentrate to have the same, or similar, functional properties as skim milk powder with reduced potential for lactose crystallization.
Manufacturing processes of milk protein concentrates are similar to skim milk powder with the use of concentrating and drying technologies intended to extract water from the skim milk. However, additional processing steps such as ultrafiltration (UF) are required prior to evaporation for the reduction of lactose, minerals, small molecules, and water. The UF membrane is designed with small pores that allow low molecular weight components (i.e., permeate) to pass through while large molecules (i.e., retentate) are prevented to pass though. As the UF is being applied, the skim milk solids concentration (i.e., retentate) increases, thereby increasing viscosity, to a point where the flux of components through the membrane will be reduced. The maximum level of concentration for the retentate is dependent upon membrane fouling and product viscosity, consequently affecting the efficiency of the process. At this point, the UF processing may be stopped and evaporation methods are employed to remove water, further concentrating the solids of the skim milk. Additional processing using UF may be done with the addition of water (i.e., diafiltration (DF)) to reestablish the flux and remove more lactose and minerals.
Inherent limitations of UF include fouling of the UF membrane. Further, UF membrane installations are capital intensive, require significant operating expense (i.e., cleaning and sanitation chemicals), increased water use, increased wastewater, and use excessive energy.
Accordingly, there is a need in the art to develop alternative processes for producing dried protein fortified milk products having similar protein concentrations as dried milk protein concentrates and skim milk powder, while having reduced lactose levels. Particularly, it would be advantageous to develop processes of producing the dried protein fortified milk products that require less or no membrane processing, less energy, and less water usage and wastewater.